It is known that the masticatory apparatus is one of the most densely nervously supplied areas of the human body and is subject to a very finely regulated control. The nerve fibers in the dentinal tubes, which partially reach up to the border between the enamel and the dentine, sense any change in load within the tooth, see in this respect Ruzicka B, Stainer M, Niederwanger A and Kulmer S: “Anatomische und funktionelle Details der Schneidezähne natürlich gewachsener unbehandelter Jugendlicher und Messwerte der Seitenzähne im internationalen Vergleich”, in “Stomatologie” May 1999: 96.3; pg. 45–53.
A naturally predetermined harmony exists between the parts in the stomatognathic system without which an undisturbed function would not be ensured. The musculature of the masticatory apparatus sensibly reacts to the load of the tooth, and by self-restriction (intra-dental proprioception) of the masticatory and biting forces it prevents the tooth from being damaged. Failures in the masticatory system lead to an increased activity of the masticatory muscles, which, if it lasts for a longer period of time, leads to a hypertrophy of the respective muscles and may even change the physiognomy of the face.
A balanced occlusion has the greatest muscular activity during pressing and grinding and delivers the highest mechanical loads for the entire masticatory apparatus. The mediotrusional contacts disturb mastication. Each additionally guiding tooth increases the muscular activity during pressing and grinding. A group guiding does obviously not change the interaction of the masticatory muscles during mastication, it does, however, change during pressing and grinding. In the case of a front-cuspid tooth guided occlusion and in a group guiding up to maximally the second premolar, only as much power is exerted during mastication as it is necessary for crushing the food. The occlusal concept of sequential guiding with front-cuspid tooth dominance therefore has the most favourable properties.
An orthodontic treatment of teeth malposition shall therefore not only be geared to aesthetic aspects, but must also take guiding of the teeth during mastication into consideration in order to avoid local load peaks leading to damage of the tooth. To reduce the loads in the masticatory apparatus, a proper occlusion with a front-cuspid tooth guiding is vitally important. The standard values of inclinations of the guide elements in the masticatory apparatus must, however, be individualized for any individual patient according to the skeletal proportions and functional parameters of the mandibular joints. However, practice has proven that the individual deviations from standard values in this respect are small. However, the dental anatomies are different from patient to patient, which is why the most different brackets are required if the guide surface angle (that is the angle between the guide elements or straight lines and the axis-orbital plane, AOP) is identical in case it is intended to correct teeth malpositions by means of these brackets.
A bracket usually has a slot of a rectangular cross section for accommodating an arch wire, which is pressed by a resilient ligature or spring onto the bottom of the slot. The angle (in technical language it is often referred to as “torque”) defined between a plane determined by the bottom of the slot and a bottom plate of the bracket to be attached to the tooth determines the torque (thus “torque”) by means of which the tooth shall be moved from a tilted malposition into a target position when using an arch wire of a rectangular or square cross section due to a positive fit between an initially twisted arch wire and the walls of the bracket slot. At the end of the treatment, this torque shall be zero, which is why the individual bracket must be chosen such that said torque angle fits to the respective tooth.
Guide elements on the teeth are such points which contact each other and slide on each other when closing the tooth rows and when moving them against each other. In the sequential guide, the guide elements successively supersede in their functions. The decrease in length and inclination of guide elements with respect to the AOP from the front over the cuspid tooth up to the premolar and molar range is characteristic for this concept, see Stainer M, Hilbe M, Leja W and Kulmer S in: “Neigung und Sequenz von Führungselementen in Gruppen geführten Okklusionen”, in Dtsch Zahnärztl. Z. 1999: 54; 325–328. The AOP is a plane in which the axis of the mandibular joint and the lower edge of the left bony orbital arch are located. The functional principle of the side tooth guide is enabled by this feature of the guide elements: each side tooth discludes on the laterotrusional side all distally following teeth and all following teeth of the mediotrusional side. The lingual surfaces and edge beads of the front teeth and cuspid teeth of the maxilla as well as the mesial edge rails and buccal cusp flanks of the premolars and molars of the maxilla apply as guide elements, see the above-cited essay of Ruzicka and others, page 46, right column bottom.
Tests on a variety of patients of the most different geographical origin, whose dentitions were measured by a 3D digitizer, revealed that the measuring points and the guide elements on the teeth determined by these measuring points substantially correspond to each other.
The determination of the correct torque angle, i.e. the correct selection of the brackets, is one of the essential procedures in the course of an orthodontic treatment, which is shared by the orthodontist as the attending physician and the laboratory doing the preliminary work for the physician. The orthodontist makes an impression of the current dentition of the patient to be treated, and the laboratory determines on the basis of a cast made from the impression the brackets required for the orthodontic treatment, which the orthodontist then attaches at predetermined positions on the patient's teeth. Up to now, the palatal tooth shape was not taken into consideration, or only to a small extent, when selecting brackets to be attached at the labial side of the teeth. Success of treatment was therefore sometimes not optimal in terms of tooth guiding. The invention intends to find a remedy in this respect.